Field of the Invention
The present invention relates to a wiring substrate for mounting thereon an electronic component such as a semiconductor device or a quartz oscillator.
Description of Related Art
There is a wiring substrate for use in a package for sealing in an electronic component such as a semiconductor device or a quartz oscillator. The wiring substrate includes an insulating substrate for mounting thereon an electronic component, and a frame which is provided on the front surface of the insulating substrate along the periphery of the surface in such a manner as to surround a mounting region for an electronic component and which defines a cavity for accommodating therein the electronic component. Usually, a sealing metallization layer is formed on an upper surface of the frame, and a via conductor is formed through the frame for connecting the metallization layer and external terminals formed on the back surface of the substrate.
In recent years, in association with a reduction in the size of an electronic component to be mounted thereon, the wiring substrate has been reduced in size. Thus, in addition to reduction in the outside dimensions (planar dimensions) of the wiring substrate to mount thereon an electronic component, the frame to define a cavity for accommodating therein the electronic component is also reduced in width. As a result, difficulty is encountered in forming a via conductor in the frame for connecting the metallization layer and external terminals formed on the back surface of the substrate.
Thus, in some conventional wiring substrates, portions other than corners of a frame are expanded in width, and via conductors are provided at the width-expanded portions, respectively (refer to, for example, Patent Documents 1 and 2).